Control devices for gas valves must be fail-safe. If the state of the control device is undefined, then it must be guaranteed that in this undefined state a gas valve controlled by the control device does not open. If, for example, a microprocessor is used as the control device for gas valves, then the use of a fail-safe circuit may help ensure that the whole arrangement is fail-safe.
Recently, piezo-operated gas valves have been used, particularly in low-voltage applications such as water heaters without a mains connection. The piezo-operated gas valves are often controlled by a control device in the form of a microprocessor. In such low-voltage applications, the supply voltage is often approximately 3 volts, which can be provided by a battery. However, a voltage of typically at least 150 volts is required to open the piezo-operated gas valves. Accordingly, a fail-safe circuit is often desirable for low-voltage applications of this kind, which, on the one hand, provides an output voltage of at least 150 volts to open the piezo-operated gas valves from a low supply voltage of approximately 3 volts, and, on the other, only generates the output voltage required to open the piezo-operated gas valves if the control device, often in the form of a microprocessor, is in a defined state to open the gas valves.